By Fredrik Dahl
VIENNA (Reuters) - When the U.N. Security Council first imposed sanctions on Iran in 2006 to try to make it halt its nuclear activity, the Islamic state had a nascent uranium enrichment program with a couple of hundred centrifuges it was testing.
Seven years later - a period which has seen the major oil producer come under increasing international punitive measures - it has installed more than 19,000 such machines for processing uranium, which can have both civilian and military purposes.
The figures, from quarterly reports by the U.N. nuclear watchdog, demonstrate Iran's determination to press ahead with a project it says is peaceful but which the West fears is aimed at developing the capability to assemble atomic bombs.
At the same time, it has amassed stocks of low- and medium-enriched uranium gas - 6.8 tons and 186 kg respectively - that experts say would be enough for several bombs if processed further to weapons-grade material.
The sanctions are taking a heavy toll on Iran's economy - its daily earnings from oil sales have tumbled 60 percent since 2011 to $100 million - but they have not stopped its nuclear push.
World powers hope to persuade Iran at talks in Geneva on October 15-16 to scale back its uranium enrichment. It is no longer considered realistic to expect Tehran to agree to suspend all enrichment, as demanded by the Security Council.
With 17 declared nuclear facilities across the country, the atomic program has "become a point of national pride", said Ali Vaez of the International Crisis Group think-tank. "Iran's nuclear program cannot be wished or bombed away."
Director General Yukiya Amano of the U.N.'s International Atomic Energy Agency (IAEA), which has inspectors in Iran almost all the time, told Reuters in June that Tehran was making "steady progress" in expanding its nuclear program and sanctions did not seem to be slowing it down.
DOUBLING OF NUCLEAR CAPACITY
Since 2006, Iran has crossed several thresholds deemed unacceptable by the West and Israel - believed to be the Middle East's only nuclear-armed power - which has threatened military strikes to ensure that its foe does not acquire such arms.
Iran built a second uranium enrichment plant at Fordow, deep underground near the Shi'ite Muslim holy city of Qom, started producing uranium to a level closer to that suitable for bombs, and installed advanced centrifuges able to enrich much faster.
Illustrating the nuclear program's growth and increasing complexity, the IAEA's reports have more than doubled in length, to 14 pages this year from just five in 2006.
Despite a more moderate tone from Iran under new President Hassan Rouhani, Vienna-based diplomats say they see no clear indication so far that Iran is putting the brakes on its nuclear drive.
Between May and August this year, it installed an additional 1,861 old-generation centrifuges at its main enrichment site near the town of Natanz, bringing the total to 15,416, although only about 60 percent of them seemed to be in operation.
At the same time, Iran completed putting in place 1,008 advanced, so-called IR-2m centrifuges at Natanz and was planning to test them, the IAEA said in a report issued in late August.
At Fordow, it continued to produce medium-enriched uranium - refined to 20 percent concentration of the fissile isotope - with 700 IR-1 centrifuges out of a total of 2,710 installed.
In addition, it has 328 IR-1 machines producing the same medium-enriched material in a research and development facility in the Natanz complex, as well as nearly 400 centrifuges of various models it is testing, including more advanced ones.
Iran's total number of centrifuges - machines that spin at supersonic speed to separate the fissile U-235 isotope - comes to over 19,800. The fact that many of them remain idle suggests that Iran could sharply ramp up production at short notice.
"Iran could quickly begin feeding natural uranium into these cascades (linked networks of centrifuges) and more than double its enrichment capacity," said David Albright of the Institute for Science and International Security think-tank.
Iran says it makes the centrifuges itself, but nuclear experts believe it likely needs to procure special components and materials for the equipment abroad, evading sanctions aimed at stopping the trade.
(Editing by Giles Elgood)